1. Field of the Invention
The invention relates to carriers for attaching a pair of magnetic heads to a rotatable head drum section of a helical scan magnetic tape unit.
2. Description Relative to the Prior Art
For high density video recording, helical tape scanning is frequently employed. In such helical-scan systems magnetic heads located on respective opposite sides of a rotatable drum section typically cooperate in pairs, on an alternating basis, in swiping across the tape to effect the overall tape scanning pattern. With this arrangement, various alignments for a head pair become critical if the recorded signal is to be "laid down" and reproduced faithfully.
For most recording systems, it is important that the heads of a head pair trace the same circle, with such heads, moreover, both being located on the same diameter of that circle. To this end, it is necessary to assure that the heads rotate in substantially the same plane (coplanarity alignment) and that the axis which extends between the head gaps is located on a diameter of the rotatable drum section (dihedral alignment).
The distance between the head tips, i.e., the diameter of the circle traced thereby, defines the protrusion of the heads beyond the rotatable drum section and represents another important alignment characteristic. The importance of head protrusion results because protrusion influences head-to-tape pressure which in turn influences head response and head water. To keep head wear low, that degree of protrusion producing the lowest head-to-tape pressure consistent with good head response is desirably maintained. Accordingly, in various situations, it may prove desirable to adjust head protrusion and, hence, the diameter of the circle traced by the heads: For example, during initial factory installation, an accurate protrusion adjustment is generally performed. Moreover, a changeover to tape having a different magnetic and/or stiffness characteristic may make a change of protrusion desirable or necessary to achieve good head response. It may also be necessary to change protrusion to compensate for head wear (in this regard, see U.S. Pat. No. 3,076,060 which describes a rather elaborate apparatus for continuous automatic adjustment of protrusion for a magnetic head).
For alignment convenience, the protrusion adjustments, as well as the dihedral and coplanarity adjustments, are desirably independent, i.e., do not influence each other. Unfortunately, the simplest way to arrange heads on a drum section, i.e., by separate fastening of each head in place, offers little independence in the alignment procedure.
Various arrangements utilizing specialized carriers for individual heads have been proposed for facilitating head adjustment, e.g., U.S. Pat. Nos. 3,207,517; 3,319,015; 3,679,838; and 3,882,543.
U.S. Pat. No. 3,422,230 describes a carrier arrangement for pairs of heads, but this arrangement apparently requires precise mating parts if correct dihedral and protrusion alignments are to be achieved without repositioning the individual heads.
What appears to be lacking in the prior art is an easily fabricated and aligned head mounting arrangement, particularly such an arrangement which provides for independent adjustments to the three basic head pair alignments.